U.S. Pat. No. 5,438,231 discloses an angular velocity sensor, a conventional resonant device which includes a body made of non-piezoelectric material, such as silicon, and having a tuning-fork shape, a lower electrode on the body, a piezoelectric member on the lower electrode, and plural upper electrodes on the piezoelectric member. A voltage applied between the lower electrode and the upper electrodes causes the tuning fork-shape body to vibrate. An angular velocity applied to the body from outside during the vibration displaces the body perpendicularly to a vibrating direction due to Coriolis force. The displacement generates a voltage between the upper electrodes and the lower electrode, and this voltage is measured as a displacement, hence allowing the angular velocity to be measured.
The angular velocity sensor including the body having the a tuning fork shape has respective resonance frequencies in a driving direction and a detecting direction of the body. The frequencies are close to each other and separated by a predetermined frequency in order to obtain a high driving efficiency and a high detection sensitivity. The resonance frequencies are determined by widths and thicknesses of arms of the tuning fork-shaped body. Those dimensions are required to be accurate with small errors thereof not more than ±1 μm.
To obtain dimensional accuracy, the body is processed in its width direction by photolithography and etching, and is processed in its thickness direction by machining. Those processes are important factors to determine absolute values of respective resonance frequencies in the width direction and the thickness direction of the body having the tuning fork-shape. Not only the absolute values of the resonance frequencies but also a difference between the resonance frequencies, i.e., a gap frequency needs to be determined to be a predetermined value.
Indexes indicating that they are the predetermined values are only shapes and dimensions of the arms, namely, widths and thicknesses of the arms while the body is processed. Therefore, it is difficult to measure actual resonance frequencies exactly. That is, it is difficult to use the gap frequency as an index for processing the body by the foregoing method.